Present battery systems in electrically driven vehicles include multiple battery modules, and each battery module includes multiple battery cells. The battery systems are designed in such a way that the individual battery cells are connected to one another in series to be able to provide the necessary high voltage of approximately 400 V. If one battery cell fails, the battery system is no longer able to supply voltage, and the vehicle becomes disabled.
In the event of a failure of a battery cell, in present designs the entire battery system must be exchanged and replaced with a new battery system. Due to the installation process for the battery system, changing individual battery modules or individual battery cells is not possible, or is possible only with a relatively high level of effort. With modified installation processes, it is expected that even replacement of individual battery modules or individual battery cells will be possible in the future. Replacing individual battery modules or individual battery cells is generally more economical than replacing the entire battery system.
Battery systems also include a battery management system, which with the aid of suitable software is capable of recognizing different states of charge of all battery cells and making a classification of the aging state of the individual battery cells. Battery cells of the battery modules recognized as defective may be indicated as such, and replaced during maintenance operations on the vehicle.
When only defective battery modules or battery cells are replaced, this results, in particular for older battery systems, in frequent trips to the repair shop and thus high maintenance costs. The costs may be reduced when other battery modules or battery cells are replaced which have a critical aging state and which will probably fail in the near future. In addition, it may be more meaningful from an economic and environmental standpoint to replace the entire battery system instead of individual battery modules or battery cells.
An optimized strategy for replacing aged battery modules or battery cells in a battery system, or the entire battery system, based on economic and environmental considerations would be desirable.
U.S. Pat. No. 9,056,556 B1 describes a method for operating a battery system in a vehicle, and a battery management system. The battery management system includes functions for modeling and predicting the performance and for operating battery modules of the battery system.
U.S. Patent Appl. Pub. No. US 2006/0284617 A1 describes a method for classifying a battery according to its aging state. In addition, a prediction of a future aging state of the battery is provided.